Repeated thermal cycleing of just about anything will shorten its life . Unless you are heating to the point of binig molten ,The object expands on startup and contraction on cool down , This introduces stress into whatevere is being heated . Eventually you get fatigue .

Basically your bending it back and forth till it breaks.

To a Blacksmith it is call tempering.

There's a name for that, but can't remember what it is. I'm sure somebody will be along in a minute and enlighten me.

New manufacture indirect heater tubes are expensive and are not dependable. I simply use older manufacture 572Bs. They last years & years and are not too expensive. Also are instant on, no warm up delay

I'll stick with my present amplifier and just turn it on when needed. Most of the time, it just sits there turned off at the switch at the back, gathering dust - till it's needed. I helps keep my desk from floating away, if we ever lose gravity in my part of the world!

I run it with the Yaesu FT-450AT with the lowest possible microphone gain (no compression) and with 24W input, it'll do just under the 400W PEP legal limit here in the UK, all day long if required. When using RTTY or SSTV, I always run it with absolutely no ALC showing on the rig's meter. This gives me around 250W-300W output on SSTV.

There is a specific transition temperate that filaments go through that causes most of the damage, its credited to the people that discovered it, and its distinct from fatigue, work hardening or annealing.

Its called the 'Miller-Larson' effect.

Its the reason vacuum tubes make use of springs to support the filaments; basically, its a transition temperature in which the filament metal goes through a 'plastic' state, resulting in grain reorientation and lengthening (and the associated thinning).

There is a specific transition temperate that filaments go through that causes most of the damage, its credited to the people that discovered it, and its distinct from fatigue, work hardening or annealing.

Its called the 'Miller-Larson' effect.

Thanks, that's the one I was thinking about, but couldn't remember the name.

New manufacture indirect heater tubes are expensive and are not dependable. I simply use older manufacture 572Bs. They last years & years and are not too expensive. Also are instant on, no warm up delay

To be frank, I'm utterly sure you're not well read enough to make such claims.

Certainly, I cannot imagine the 3CPX800A7 and 3CPX1500A7/8877 tubes would have seen such widespread usage in medical applications if a couple of 572Bs (a tube that even when first made was begging for a use) would have sufficed; offering better reliability and lifetime.

I've encouraged you previously to read more; I understand if there is a specific reason this cannot be achieved, but if that is indeed the case, please don't pollute these forums with ridiculous claims.

In another thread recent thread (the AL-572 one) you misquoted someone else as saying 572Bs are rated as 10,000 hours. When I responded to that person stating that their claim was ludicrous, they politely pointed out they never made such a statement. I then checked the thread, and they indeed had not.

Whilst I bear some responsibility for not fact checking before posting, your actions directly lead to me having to sincerely apologise to another member of these forums. I did not appreciate having to do that, and having been made a fool of.

Simply put, that is unacceptable; and a complete violation of the Ham ethos of self education and helping one another.

At this point - in the interests of the community - I am obliged to recommend others question your statements and advice, lest they appear foolish or do something stupid and potentially dangerous.

Certainly, I cannot imagine the 3CPX800A7 and 3CPX1500A7/8877 tubes would have seen such widespread usage in medical applications if a couple of 572Bs (a tube that even when first made was begging for a use) would have sufficed; offering better reliability and lifetime.

I have little doubt that reason they use the ceramic valves is because of higher power output, more compact design, more rugged in handling/replacing, ducted cooling that allows tube heat to be discharged outside of unit without heating chassis, frequency range of tube and list goes on. I seriously doubt that filament life is part of choice logic because in medical use they swap them long before they get close to rated life. Operating parameters are the determining factor here.

Logged

--------------------------------------Ham since 1969.... Old School 20wpm REAL Extra Class..

External anode tubes also cost more, with Eimacs especially as there is about a 2:1 price difference between and Eimac provided tooling/training to the Chinese, but allow "serious" power without the frequency limitations of a huge glass tube. The 3-500G seems to be the current glass tube transition point of cost per Watt. The 2000T was about the largest of the 30's designed internal anode triodes and was maxed out at a measly 5400W in AM service.

Lack of new products has rendered tubes such as the 3-1000Z and 4-1000A to the expensive low volume replacement market, new old stock, Fleabay, and hamfests.

Certainly, I cannot imagine the 3CPX800A7 and 3CPX1500A7/8877 tubes would have seen such widespread usage in medical applications if a couple of 572Bs (a tube that even when first made was begging for a use) would have sufficed; offering better reliability and lifetime.

I have little doubt that reason they use the ceramic valves is because of higher power output, more compact design, more rugged in handling/replacing, ducted cooling that allows tube heat to be discharged outside of unit without heating chassis, frequency range of tube and list goes on. I seriously doubt that filament life is part of choice logic because in medical use they swap them long before they get close to rated life. Operating parameters are the determining factor here.

So let me get this straight; you're suggesting that a tube with:A more compact designMore rugged in handlingBetter coolingAnd a list that goes on

Is going to have worse filament life than a poor QC control 811A. Have you even seen the photos of the Shu Guang plant and the complete lack of cleanliness?

Irrespective, "filament life" is not the issue, internet element poisoning due to poor manufacturing standards and materials is.

Just ask Carl (or any other amp repairer) how many ceramic tubes he's replaced over the years compared to glass envelop tubes. There simply is no lifetime comparison.

For one, more compact = less gas = less potential for filament poisoning.

CT / MRI machines are left on 24/7, do you REALLY think they replace tubes every 1500-3000 hours?! Of course lifetime is a design consideration!!!!!!

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